Urban agriculture: The potential and challenges

MADISON, Wis. — As the concept of local food and urban gardening gains popularity, urban agriculture, with its benefits and obstacles, is coming to many cities. But the challenges growers face must be understood and addressed if urban gardens are to become widespread and even profitable.

On the plus side

The benefits of urban agriculture are many. Urban gardens are often built on previously unused lots, increasing the beauty and value of the neighborhood. They provide recreation opportunities and a social network for the gardeners involved.

Urban food production also means that healthy, fresh produce is readily available to city dwellers.

The down side

But several obstacles face planners and growers, too, say Sam Wortman, assistant professor at the University of Illinois at Urbana-Champaign and Sarah Taylor Lovell, in a new paper they authored.

The down sides include soil contaminants, water availability, and changes in climate and atmospheric conditions, and that doesn’t even address production, labor or marketing issues.

Heavy metals

Several contaminants can be found in urban soils, and lead is the most prevalent. While there is concern about plants taking up lead from soils, research suggests that they actually take up very little.

“Even in roots, there is still a relatively small amount of lead compared to, for example, what we’re exposed to from drinking water,” said Wortman.

Direct ingestion of soil containing lead is a bigger threat than plant uptake. Soils can be directly ingested when children play in and eat soil, soil adheres to crops after they’re harvested, or soil particles blow in the air.

Practices such as washing food well before eating and covering soils with mulch can help decrease these risks.

Water sources

Finding reliable and safe water sources can be difficult for urban farmers. Technologies such as drip irrigation that precisely deliver water where and when it’s needed can help conserve water.

Reusing rainwater and wastewater can provide additional water, but those sources must be monitored for contaminants, and perhaps treated.

Climate differences

Changes in atmospheric and climate conditions in cities compared to rural areas can also be obstacles for urban growers.

For example, temperatures and vapor pressure deficits (the difference between saturated and actual vapor pressure at a specific temperature) are often higher in cities, the authors say.

Extreme temperatures during the day and higher nighttime temperatures can inhibit photosynthesis in plants and decrease yields.

Likewise, when vapor pressure deficits are higher, plants have to use more water creating moisture stress and reducing photosynthesis.

More research

To better understand the effects of varying climates and atmospheric states on food production, Wortman and his colleagues have a project underway.

They are looking at six sites on a gradient from downtown Chicago to 40 miles west of the city. The sites all have the same, ideal soil conditions allowing the researchers to take soil factors out of the equation.

“We are trying to isolate the effects of the atmosphere,” explained Wortman. “We are monitoring concentrations of carbon dioxide, ozone, temperature, humidity, wind, and other factors across all of the sites.”

Early results

The study is still ongoing, but Wortman said the preliminary results show crop yields are highly variable at the different sites, with some crops growing better closer to the city center and others producing higher yields in more rural areas.

Wortman hopes to identify crops that grow well in any given urban environment. It may then be possible to develop new crops that are adapted to urban gardens and customized for the area.

Bigger impact

“We’re looking at it from a very practical perspective of providing recommendations for urban farmers, but it also has an angle of how these different crops respond to altered environments,” said Wortman.